The etiology and pathogenesis of AAA is poorly understood. The hypothesis to be tested in grant is whether an antigen-driven T-cell response may be responsible for the initiation (and may contribute to the propagation) of AAA, and whether these T cells recognize host antigens. Our specific aims are: 1. To determine whether fresh (not expanded in culture) T cells infiltrating AAA lesions of patients with spontaneous or inflammatory AAA, contain substantial proportions of monoclonal T cells. To identify clonally expanded alpha-, beta-, gamma- and beta-chain TCR transcripts employed by the TCRs of these T cells. 2. To identify the antigens recognized by T cells employing the clonally expanded alpha- and beta-chain TCR transcripts in AAA inflammatory cell infiltrates. a. To express the clonally expanded in AAA infiltrates TCR transcripts into alpha beta TCR-negative into alpha beta J.RT3-T3.5 Jurkat cells by transfection, or into normal cytotoxic T-lymphocyte (CTL) lines by infection with retroviral vectors. b. To determine whether these transduced or transfected T cells with the clonally expanded TCR, recognize putative AAA antigens (elastin, oxidized LDL, AAA-P, collagen types I and III, and CMV). 3. To further define the functionality of the entire AAA T-cell infiltrate and to ensure that functionally responsive T-cell clones are obtained, we will develop by limiting dilution T-cell clones specific for putative AAA antigen(s) (elastin, oxidized LDL, AAA-P/MAGP-36, collagen types I and III, and CMV). a. To fully characterize these T-cell clones. b. To compare the TCR sequences used by these T-cell clones to those of fresh (not expanded in culture) AAA infiltrating T cells from the same patients, in order to determine whether clonal populations of these fresh infiltrating T cells have the same antigenic specificities to those of antigen-specific T-cell clones. 4. To investigate the production of chemokines and Th1 and Th2 cytokines in AAA lesions (transcripts and proteins) and to identify the individual cell types producing these molecules. To correlate the degree of infiltration, the activation stage of the infiltrating T cells, the presence of oligoclonal populations of T cells and the production of chemokines and cytokines in AAA lesions with the findings of the second RO1 research grant application of this Interactive RO1 Program and, in particular, with: (i) Morphological and spatial alterations in the aneurysm; (ii) Biomechanical properties of the aneurysm.